1. Field of the Invention
This invention relates to a heavy duty pneumatic radial tire, and more particularly to a heavy duty pneumatic tire for use in heavy vehicles such as truck, bus and the like capable of sufficiently developing excellent bead portion durability without additionally arranging extra reinforcing members in a bead portion for reducing the weight of the bead portion.
2. Description of Related Art
In the pneumatic radial tires used in heavy vehicles such as truck, bus and the like, there is a serious problem that failures in the bead portion typified by separation from a turnup end of a carcass ply and separation from an end of cord in a bead portion reinforcing cord layer are caused to obstruct a complete service life of a new tire and bring about troubles in repetitive recapped use. Up to the present, therefore, there are proposed and practiced various countermeasures for solving the above problem.
A large number of these countermeasures lie in the use of many bead portion reinforcing cord layers or the increase of volume in the bead portion as a whole for reducing falling-down of a bead portion connected to a ground contact region toward the outside of the tire during the running under a load as far as possible to reduce strain acting to an end of a bead portion reinforcing cord layer or a turnup end of a carcass, and hence they follow the increase of tire weight and the rise of cost. However, they are at a state not corresponding to current demands such as weight reduction, cost reduction and the like.
Further, these countermeasures are utterly impossible to meet demands of resource-saving and energy-saving and requirement of reducing production cost. As a result of examining a portion of the tire capable of reducing tire weight, there is no longer a portion other than a bead portion. For this end, it is attempted to prepare a trial tire for truck and bus by selecting a bead core as a most possible target for reducing the weight, decreasing the winding number of steel wires constituting the bead core, and also decreasing a weight of rubber for the enhancement of bead portion rigidity called as a stiffener rubber taperingly extending outward from an outer peripheral surface of the bead core in a radial direction of the tire, which is mounted onto a vehicle and subjected to an actual running test.
In this test, the trial tire inflated under a given internal pressure becomes large in so-called falling-down deformation under loading and hence a large xe2x80x9csettlingxe2x80x9d phenomenon is caused in the bead core as the running distance of the tire becomes long. The whole shape of the bead portion is largely deformed from that of the new tire accompanied with the above phenomenon and consequently it has been confirmed that strain acting to a radially outward end of a bead portion reinforcing steel cord layer required for maintaining the durability of the bead portion is increased to cause separation failure.
In JP-B-1-26884 is disclosed a heavy duty pneumatic radial tire wherein a single metal cord reinforcing layer is disposed outside the turnup portion of the radial carcass ply and a cord arranging angle in an upper end portion of the reinforcing layer is not more than 20xc2x0 with respect to the circumferential direction of the tire and a cord arranging angle in a region ranging from a start point of contacting with a flange of a rim toward a bead base is made larger by not less than 10xc2x0 than the above angle at the upper end portion as a bead portion structure capable of maintaining and improving the durability even when the weight is reduced by decreasing the stiffener rubber likewise the above case.
Even in such a tire, however, it has been confirmed that the separation resistance is insufficient in the upper end portion of the metal (steel) cord. As a result of examinations on such a cause, it has been elucidated that the upper end portion of the metal cord reinforcing layer can not sufficiently follow the deformation at stepping-in side and kicking-out side of the ground contact region of the tire tread in the radial direction of the tire during the running under loading and hence a large strain is created in the upper end portion to cause the separation failure.
Another means for improving the bead portion durability without so increasing the tire weight is proposed in JP-A-59-216709. In this case, as shown in FIG. 13, a metal cord layer as a reinforcing layer for a bead portion 1 is divided at inside and outside of a bead core 3 into an outer metal cord layer (protection layer for end of turnup portion 4t) 15a and an inner metal cord layer (support reinforcing layer) 15b, respectively, noticing xe2x80x9csettlingxe2x80x9d of the bead core in addition to falling-down of the bead portion. Further, modulus at 1% elongation of the layer 15a is made smaller than that of the layer 15b and an inclination cord angle of each layer with respect to the radial plane of the tire on a circumference passing an upper end of the layer is within a range of 45-70xc2x0 at maximum (20-45xc2x0 with respect to the circumference of the tire), whereby the improvement of the bead portion durability is attained.
Since the bead portion reinforcing layer is divided into the protection layer 15a for turnup 4t end and the support reinforcing layer 15b (division ends P, Q of the layers 15a, 15b), the restraint by the ends 15ae, 15be of the layers at positions contacting with a rim is considerably moderate as compared with a case of using a single layer, and the layers 15a, 15b are easy to follow the remarkable shearing deformation in the circumferential direction of the tire at both stepping-in and kicking-out sides of the tread during the running of the tire under loading, and hence the concentration of strain acting to an outer end portion of each layer in the radial direction of the tire is largely mitigated.
Recently, a tendency of forming a lower section profile of a heavy duty pneumatic radial tire, particularly truck or bus tire more proceeds and hence an internal air pressure becomes higher and conditions input to the bead portion becomes more severer. In the aforementioned division of the bead portion reinforcing layer into the metal cord layers 15a and 15b at inside and outside of the bead core 3, the clamping force to the metal cord layers 15a, 15b between the bead core and the flange and bead sheet of the rim is hardly expected as previously mentioned, so that both the metal cord layers 15a, 15b are easily moved in the bead portion 1 at a ground contact region during the running of the tire under loading, which simultaneously causes the following problems.
When the tire is inflated under a higher internal pressure, a large tension is applied to the carcass ply 4 as shown by an arrow T in FIG. 13. That is, the tension T is a force of drawing out the carcass ply 4 from the bead core 3 in a direction shown by the arrow. Particularly, when the bead portion 1 is fallen down toward the outside of the tire under loading, the carcass ply 4 acts to largely rotate the bead core 3 around a graphic center of gravity g at a section of the bead core in a direction shown by an arrow r together with the force T and the moving easiness of the metal cord layers 15a, 15b. This action is applied to the bead core 3 every one rotation of the tire and the temperature of the bead portion 1 becomes high during the running of the vehicle, so that xe2x80x9csettlingxe2x80x9d deformation as a plastic deformation is caused in the bead core 3 and the deformation degree proceeds as the running distance of the tire becomes long.
Such a large xe2x80x9csettlingxe2x80x9d deformation of the bead core 3 largely changes the sectional shape of the bead portion 1 from a new tire state. As a result, the deformation of the bead portion brings about such a inconvenience that the bead portion reinforcing metal cord layer 15a located outside the turnup portion 4t of the carcass ply largely diverts from an arrangement of previously minimizing strain acting to the outer end portion of the layer in the radial direction of the tire and hence a large strain is concentrated in the vicinity of the outer end 15ae of the metal cord layer 15a and the separation failure is apt to be caused in this end portion.
And also, even in a tire having a more reduced weight by decreasing the winding number of steel wires constituting the bead core, it has been confirmed that if it is intended to locate the division position between the metal cord layers 15a and 15b as a bead portion reinforcing layer in a position separated away outward from the periphery of the bead core 3 in the radial direction of the tire, the degree of xe2x80x9csettlingxe2x80x9d deformation in the bead core becomes large, which brings about the same large change of the bead portion shape as in the above case and hence the separation failure is caused in the outer end portion of the metal cord layer and the given service life of the tire can not be attained.
It is, therefore, an object of the invention to provide a heavy duty pneumatic radial tire having a light weight and a bead portion durability equal to or more than that of the conventional heavy duty pneumatic radial tire even when the winding number of steel wires in the bead core is decreased and the volume of rubber in the bead portion, particularly stiffener rubber is decreased accompanied therewith irrespectively of a tube-containing tire or tubeless tire.
According to a first aspect of the invention, there is the provision of a heavy duty pneumatic radial tire comprising a carcass of one or more rubberized cord plies extending between a pair of bead cores each embedded in a bead portion and containing cords arranged along a plane inclusive of a rotating axial center of the tire, at least one of which plies being wound around the bead core from inside of the tire toward outside thereof to form a turnup portion, and a bead portion reinforcing layer comprised of a single rubberized steel cord layer covering a surface of the carcass ply over a region ranging from an outer position of the turnup portion in a radial direction of the tire along an outer surface of the turnup portion through the bead core up to an inside of the tire, in which an inclination angle of steel cord in the bead portion reinforcing layer with respect to a circumferential line of the tire is within a range of 22-35xc2x0 in outermost end portions outside and inside the tire in the radial direction and an inclination angle of steel cord outside and inside of the tire in the vicinity of a straight line passing through a graphic center of gravity in the bead core at a section thereof and in parallel to the rotating axis of the tire is within a range of 5-50xc2x0 added to the inclination angle range of the above outermost end portion.
This tire comprises a pair of sidewall portions connecting to the pair of bead portions, a tread portion extending between both the sidewall portions, a belt reinforcing the tread portion on an outer periphery of the carcass and comprised of two or more cross cord layers, preferably two or more two cross steel cord layers according to custom. When the carcass is one ply, it is adaptable to use a rubberized steel cord. And also, the cords of the carcass ply are arranged perpendicular or substantially perpendicular to an equatorial plane of the tire in the tread portion. The word xe2x80x9cinclination angle with respect to circumferential line of the tirexe2x80x9d used herein means an angle defined between tangents of circumferential line and steel cord axial line at an assumption intersect of circumferential line at a given position (assumption line) and the cord axial line.
In a preferable embodiment of the first aspect of the invention, the inclination angle of steel cord outside and inside of the tire in the vicinity of a straight line passing through a graphic center of gravity in the bead core at a section thereof and in parallel to the rotating axis of the tire is within a range of 5-30xc2x0 added to the inclination angle range of the outermost end portion with respect to the circumferential line of the tire.
In the tire according to the invention, it is possible to add an organic fiber cord layer such as nylon cord layer or the like to the bead portion reinforcing layer so as to cope with a severer load or a requirement of increasing the recapping number among use conditions of the tire. For this purpose, it is favorable that one or more organic fiber cord layers are arranged around an outer surface of the bead portion reinforcing layer. In this case, it is desirable that a direction of arranging steel cords in the bead portion reinforcing layer is the same as a direction of arranging cords in the organic fiber cord layer.
Considering the productivity of the tire, it is favorable that a ratio of 100% modulus of a coating rubber for steel cord in the bead portion reinforcing layer to 100% modulus of a coating rubber for cord in the carcass ply is within a range of 0.6-1.0. On the other hand, considering the improvement of tire performances in addition to the tire productivity, it is desirable that the ratio of 100% modulus of a coating rubber for steel cord in the bead portion reinforcing layer to 100% modulus of a coating rubber for cord in the carcass ply is within a range of 0.6-0.9. In the other preferable embodiment of the first aspect of the invention, a group of arranging two or more steel cords side by side is used as an arrangement of steel cords in the bead portion reinforcing layer.
According to a second aspect of the invention, there is the provision of a heavy duty pneumatic radial tire comprising a carcass of one or more rubberized cord plies extending between a pair of bead cores each embedded in a bead portion and containing cords arranged along a plane inclusive of a rotating axial center of the tire, at least one of which plies being wound around the bead core from inside of the tire toward outside thereof to form a turnup portion, and a bead portion reinforcing layer comprised of separately independent rubberized steel cord layer segments covering the carcass ply inclusive of its turnup portion in the bead portion, in which said bead portion reinforcing layer is comprised of two independent rubberized steel cord layer segments arranged at outside and inside regions of the bead portion putting the bead core therebetween, and an outer end of the independent rubberized steel cord layer segment located at the outside region of the bead portion in the radial direction of the tire extends upward over an end of the turnup portion of the carcass ply, and opposed ends of the two rubberized steel cord layer segments are arranged so as to adjoin each other in the vicinity of the bead core, and an inclination angle of steel cord in the two independent rubberized steel cord layer segments arranged at outside and inside regions of the bead portion putting the bead core therebetween with respect to a circumferential line of the tire is within a range of 15-30xc2x0 in an outer end portion of each of the two rubberized steel cord layer segments in the radial direction of the tire and an inclination angle of steel cord in an inner end portion in the radial direction of the tire is within a range of 35-60xc2x0 in at least one of the two rubberized steel cord layer segments.
The term xe2x80x9cvicinityxe2x80x9d in the vicinity of the bead core means a partial gathering of all points wherein a distance from an arbitrary point I is smaller than a certain value in metric space, while the term xe2x80x9carbitrary point Ixe2x80x9d means all points existing on the bead core at section thereof. And also, the term xe2x80x9ccertain value of the distance from the point Ixe2x80x9d means a value that a distance measured from a point on a surface of the bead core in all directions is within a range of 0.5-20 mm. Furthermore, the term xe2x80x9cadjoin each otherxe2x80x9d used herein includes a case of slightly separating away the opposed ends from each other in addition to a case of contacting the opposed ends with each other.
In a preferable embodiment of the second aspect of the invention, the opposed ends of the two rubberized steel cord layer segments as the bead portion reinforcing layer are butted to each other. In this case, the butting position between the opposed ends is existent around the bead core.
In another preferable embodiment of the second aspect of the invention, the steel cords of the two layer segments located at the outside and inside regions of the bead portion are arranged in the same inclining direction with respect to a radius line of the tire.
In the other preferable embodiment of the second aspect of the invention, the steel cords of the two layer segments are arranged in an inclining direction opposite to each other with respect to a radius line of the tire.
In a still further preferable embodiment of the second aspect of the invention, when a 15xc2x0 drop center rim or a wide-width flat base rim is used, the adjoining position between the opposed ends of the two rubberized steel cord layer segments as the bead portion reinforcing layer is existent between a straight line passing through a graphic center of gravity in the bead core at section thereof and perpendicular to the rotating axis of the tire and a normal line drawn from an outermost end of a surface of the bead portion contacting with a flange of a rim in the radial direction of the tire to the carcass ply facing the inside of the tire. This type of the tire is a radial ply tire for truck and bus, in which a tire using the 15xc2x0 drop center rim is a tubeless tire and a tire using the wide-width flat base rim as an approved rim is a tube-containing tire. Moreover, the term xe2x80x9coutermost end in the radial direction of the tirexe2x80x9d used herein means a position when the tire is assembled onto the approved rim and inflated under a maximum air pressure corresponding to a maximum load capacity of the tire defined in xe2x80x9cair pressure-load capacity tablexe2x80x9d according to the above standard.
According to a third aspect of the invention, there is the provision of a heavy duty pneumatic radial tire comprising a carcass of one or more rubberized cord plies extending between a pair of bead cores each embedded in a bead portion and containing cords arranged along a plane inclusive of a rotating axial center of the tire, at least one of which plies being wound around the bead core from inside of the tire toward outside thereof to form a turnup portion, and a bead portion reinforcing layer comprised of separately independent rubberized steel cord layer segments covering the carcass ply inclusive of its turnup portion in the bead portion, in which said bead portion reinforcing layer is comprised of three independent rubberized steel cord layer segments consisting of an inner reinforcing layer segment arranged at an inside region side the carcass ply facing the inside of the tire, an outer reinforcing layer segment arranged at an outside region side the turnup portion of the carcass ply, and a middle reinforcing layer segment arranged around the bead core between the inner reinforcing layer segment and the outer reinforcing layer segment, and an outer end of the outer reinforcing layer segment in the radial direction of the tire extends over an end of the turnup portion of the carcass ply, and opposed ends among the three rubberized steel cord layer segments are arranged so as to adjoin each other in the vicinity of the bead core, and an inclination angle of steel cord in the bead portion reinforcing layer with respect to a circumferential line of the tire is within a range of 15-30xc2x0 at an outer end portion of each of the outer and inner reinforcing layer segments in the radial direction of the tire and within a range of 35-60xc2x0 at an inner end portion thereof and an inclination angle of steel cord in the middle reinforcing layer segment is made larger than the inclination angle of steel cord at the inner end portion of each of the above outer and inner reinforcing layer segments.
In a preferable embodiment of the third aspect of the invention, the steel cords in at least two layer segments among the three reinforcing layer segments as the bead portion reinforcing layer are arranged in the same inclining direction with respect to a radius line of the tire.
In another preferable embodiment of the third aspect of the invention, a group of arranging two or more steel cords side by side is used as a steel cord in at least one layer segment among the three reinforcing layer segments as the bead portion reinforcing layer.
In a preferable embodiment of the second and third aspects of the invention, a coating rubber for steel cords in a layer segment arranged in at least the outer region of the bead portion has 100% modulus smaller than that of a coating rubber for cords in the carcass ply.
In another preferable embodiment, at least one organic fiber cord layer is arranged so as to cover an outer surface of the bead portion reinforcing layer when at least one of load and running speed as a service condition is severe.